Effects of W/Ni co-doping on the structural, magnetic, electrical, and optical properties of Aurivillius phase Bi₅FeTi₃O₁₅ ceramics

We investigate the influences of W/Ni co-doping on the structural, magnetic, electrical, and optical properties of four-layered Aurivillius Bi₅FeTi₃O₁₅ ceramics. All the specimens can be indexed with the orthorhombic structure and the space group of A2₁am. The incorporation of W/Ni significantly promotes the grain’s growth and compactness. Compared with the antiferromagnetic state in pure sample, a weak room-temperature ferromagnetic state is found in the doped samples. The dielectric relaxations in samples with x ≤ 0.1 follow with Vogel–Fulcher relation and can be ascribed to the fluctuation behavior of local polarization, whereas the dielectric relaxation in sample x = 0.15 obeys well Arrhenius law and is due to the localized hopping process of electrons. The piezoelectric measurements indicate that the composition x = 0.05 represents the largest d₃₃ value of 14pC/N at room temperature, which can be attributed to the optimal conductivity. In addition, all the compositions have two absorption edges with the direct inter-band transition due to the electron excitation from the hybridized Bi 6s + O 2p + Fe t_2g valence band to Fe e_g and Ti 3d conduction bands.